1. Field of the Invention
The present invention relates to a droplet discharge head which discharges liquid from a nozzle opening and an image-forming apparatus.
2. Description of the Related Art
An ink jet recorder including a droplet discharge head which discharges droplets of ink, for example, is known as an image-forming apparatus such a printer, fax machine, copier, plotter, or complex machine in which some of these are combined. The ink jet recorder is configured to form an image by adhering ink drops to a sheet while feeding a medium. The medium here is not limited to a sheet, and can be a medium to be recorded, recording medium, transfer material, recording sheet or the like. Moreover, the image-forming apparatus is intended to be an apparatus which discharges liquid to a medium such as paper, string, fiber, fabric, leather, metal, plastic, glass, wood, or ceramics to form an image. The image-formation is intended not only to apply an image having characters, shapes or the like to a medium but also to apply an image without having a pattern or the like to a medium (to simply discharge droplets). The term ink is not limited to so-called ink, and it can be used as a generic name of liquid including, for example, a DNA sample, resist, or pattern material as long as it becomes liquid when it is discharged.
The ink jet recorder includes an ink jet head. In this ink jet head, a liquid chamber-forming substrate is sandwiched between a nozzle plate and an actuator substrate, and these plate and substrates are bonded. The nozzle plate is provided with a plurality of nozzle openings which discharges ink drops. This ink jet head is attached to a head housing. A liquid chamber such as a common liquid chamber or a pressurized liquid chamber, which communicates with the nozzle opening, is formed in the liquid chamber-forming substrate in accordance with each nozzle opening. The actuator substrate includes a pressure generator which changes pressure in the pressurized liquid chamber and a vibration plate which applies deformational displacement by a pressure generator to ink in the pressurized liquid chamber. The pressure in the pressurized liquid chamber is changed by the pressure generator so that the ink drops are discharged from the nozzle opening. On the other hand, the nozzle plate or the vibration plate is made of a metal material such as stainless steel. There is a difference between a linear expansion coefficient of a resin material for use in the liquid chamber-forming substrate and a linear expansion coefficient of a metal material for use in the nozzle plate or the vibration plate. For this reason, the liquid chamber-forming substrate bends due to a change in an environmental temperature or an operation temperature in the ink jet head formed by bonding the nozzle plate, liquid chamber-forming substrate, and vibration plate. An ink jet head described in JP2003-053966A having a configuration which prevents the bending of the liquid chamber-forming substrate is known.
The ink jet head in JP2003-053966A includes a nozzle plate, flow passage-forming substrate, and actuator substrate. The nozzle plate is provided with a plurality of nozzle openings. The flow passage-forming substrate is provided with a weir and a partition. The weir is used to form an ink flow passage including a pressured liquid chamber which is bonded to the nozzle plate to communicate with the nozzle opening, a common liquid chamber to which ink which is supplied to the pressured liquid chamber is supplied, and a flow passage which communicates the pressured liquid chamber and the common liquid chamber. The partition is used to zone the ink flow passage which is formed in accordance with a plurality of nozzle openings, and an ink flow passage in accordance with the adjacent nozzle openings. The weir and the partition are made of a resin material because they require a highly accurate process for forming the pressured liquid chamber and the flow passage. There is a difference between a linear expansion coefficient of the resin material of the weir and the partition and a linear expansion coefficient of the metal material of the nozzle plate and the vibration plate bonded to the weir and the partition. For this reason, the flow passage-forming substrate including the weir and the partition bends in the thickness direction due to a change in an environmental temperature or an operation temperature. In order to control such bending, the rigidity of the flow passage-forming substrate including the weir and the partition is improved by burying a metal plate as a reinforcement material in the resin member of the weir and the partition constituting the flow passage-forming substrate. A phenomenon in which the flow passage-forming substrate bends due to a change in environmental temperature or operation temperature is thereby controlled.
However, the size of the ink jet head in JP2003-053966A is increased for the following reasons because the metal plate is buried in the weir and the partition of the resin material in the flow passage-forming substrate.
An insert-molding method is used for manufacturing the flow passage-forming substrate in which the metal plate is buried in the weir and the partition of the resin material. In order to form the flow passage-forming substrate by the insert-molding method, at first, the metal plate is loaded in an injection-molding mold. A melted resin material is injected in a cavity which is a space between the metal plate and the injection-molding mold provided around the metal plate. After the resin material is set, the flow passage-forming substrate is removed from the injection-molding mold. However, the resin material is not injected when the space between the metal plate and the injection-molding mold provided around the metal plate is narrow, and the weir and the partition in the flow passage-forming substrate may not be formed in sufficient shapes. In order to form the weir and the partition of the flow passage-forming substrate into sufficient shapes, it is necessary to set the space between the metal plate and the injection-molding mold provided around the metal plate to a predetermined size or more such that the melted resin material is sufficiently injected in the cavity. With this configuration, the thickness from the inner wall surface which forms the ink flow passage with the portion of the resin material in the weir and the partition to the surface of the buried metal plate becomes a prescribed thickness or more corresponding to a size which is a predetermined size or more of the space.
In contrast, the size of the metal plate buried in the weir and the partition of the resin material cannot be reduced to be smaller than a predetermined size because it is necessary to ensure the rigidity of the metal plate. Specifically, since it is necessary to control the bending of the ink flow passage in the longitudinal direction, the length of the metal plate in the longitudinal direction which is the same as the longitudinal direction of the ink flow passage cannot be reduced. The thickness of the metal plate cannot be reduced because it is necessary to ensure the rigidity of the metal plate member. As described above, the metal plate is required to be a prescribed size and the thickness of the metal plate cannot be reduced so as to ensure rigidity. A metal plate whose size cannot be reduced to be smaller than a predetermined size is buried in the portion of the resin material in the weir and the partition as described above. For this reason, the size of the flow passage-forming substrate when the metal plate is buried in the resin member is increased to be larger than the size of the flow passage-forming substrate when the metal plate is not buried.
As described above, in the ink jet head in JP2003-053966A, the bending of the flow passage-forming substrate can be controlled by improving the rigidity of the flow passage-forming substrate, but the ink jet head is increased in size.